This may sound terribly pessimistic but there really is no such thing as an 'original' plot. Is your main character male? OH NO IT'S BEEN DONE! *shrug*
I actually stress alot about originality and doing something that's "never been done" and all it does is detract from what you should be doing. And that's enjoying yourself. For me, I write what I would do. If I were in an awesomely epic fantasy story that is. What interests me? What plights would I never want to tackle? What situations would be entertaining? What would I find incredibly romantic or horrific or frightening? For me, a story is one amazing daydream that I get to share with everyone.
You can't really concentrate on what other people will like 'cuz you can't please everyone, so just concentrate on pleasing yourself. Everyone else can join you if you they want. (Dear jebus that sounds TERRIBLE and I can't think of an other way to rephrase it.)
I've seen alot of suggestions that fall along the line of, get your character and make life living hell for them, I don't think it's really about that (though anyone who knows me and my writing would beg to differ lol). Not every story can be about tackling your greatest fear, maybe it's the fear you didn't know you had (I mean...if it is your greatest fear wouldn't you think to stay away from it? Just saying.) Besides, if your main concentration is torturing your characaters, you have no connection with them. You're the bully pouring lighter fluid down the anthill, you need to be one of the ants. The more in tune with your characters you are, the more it shows, the more realistic they seem, and the easier it is for everyone else to fall in love with them. (I think.) Not to say all the characters need to be knights in shining armor. There's a character in my book that I HATE. Hate, hate HATE. Everytime I wrote a scene with him I was like OMG, Why aren't you
dead yet? And everyone who read the story felt the same way. It was that much more satisfying when my muse finally let me kill him.
My advise? Pick one, maybe two goals, and stick to them. When I wrote my first novel, which happened to have vampires in it, surprise surprise, my first goal was to challenge EVERY vampire/romance stereotype I possibly could and go in the other direction. My second goal was to keep moving forward. You know how you write a chapter and realize you can't do a,b, or c, in this scene 'cuz there was something you didn't mention four chapters ago? Screw it. Don't do the scene then, come up with something else. It's the urge to go back and re-work everything to fit this one thing that creates plot holes and disrupts the fluidity. It's hard, I'll admit, but I think my story is actually better for it. After all, if it didn't fit when I first conceived the chapter that I've already finished and loved enough to move on, why go back and add stuff?
Man....long post is LONG. I'll zip up now.